1. Field of the Invention
The present invention relates to a travel control system for a vehicle which causes the vehicle to follow a preceding vehicle at a predetermined inter-vehicle distance in a low vehicle speed region.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2002-319100 (JP '100) discloses a travel locus estimating system which estimates a future travel locus of a subject vehicle based on a yaw rate and a speed of the vehicle. In the disclosed system, to compensate for a decrease in the accuracy of estimating the travel locus due to a decrease in the accuracy of detecting the yaw rate at a lower vehicle speed, such as when the vehicle is being started, an estimated travel locus before stoppage of the subject vehicle is stored. As such, when the subject vehicle is started after the stoppage, a following-travel control of the subject vehicle is performed using the stored estimated travel locus, wherein the subject vehicle is able to follow a preceding vehicle.
In general, the following-travel control system, disclosed by JP '100, has problems that are described below.
In particular, FIG. 5A illustrates a situation where a preceding vehicle is stopped at a position slightly forward of an entrance of a curved course, and a subject vehicle traveling behind the preceding vehicle is stopped at a leading end of a straight course before the curved course. As shown in FIG. 5B, a driver of the subject vehicle turns on a switch for starting the following-travel control system which causes the subject vehicle to automatically travel at a predetermined inter-vehicle distance and initially follow the preceding vehicle at a low speed. At this time, the subject vehicle is at the leading end of the straight course before the curved course, and thus, a travel locus of the subject vehicle is estimated to extend straight forward. Therefore, the preceding vehicle, which is displaced to the right of the estimated travel locus, is not recognized as a preceding vehicle, and an object along the road, such as, for example, a reflecting plate provided on a guard rail, is erroneously recognized as the preceding vehicle.
When the driver of the subject vehicle turns on the switch for starting the following-travel control system in this state to start the subject vehicle, because the object along the road is erroneously recognized as the preceding vehicle, the subject vehicle is immediately decelerated and stopped in order to maintain the predetermined inter-vehicle distance to the object along the road, wherein the subject vehicle is not able to properly follow the actual preceding vehicle.
Thereafter, the subject vehicle enters the curved course and begins turning to the right. As a result, as shown in FIG. 5C, the travel locus of the subject vehicle is estimated to be to the right in the forward direction, that is, the preceding vehicle is correctly recognized as the actual preceding vehicle wherein the following-travel control system begins to properly target the actual preceding vehicle.
Accordingly, in the system disclosed by JP '100, the movement of the subject vehicle becomes jerky when starting the following-travel control at the time the preceding vehicle begins to travel, resulting in a very high probability that a proper and smooth starting of the subject vehicle is hindered.